1. Field of the Invention
The invention relates to a curve-tilting vehicle having means for laterally tilting at least one section of the vehicle about a tilting axis running essentially parallel to the vehicle's longitudinal axis, to the effect that while traveling, for instance in a bend or on sloping or uneven ground, the center of gravity of the vehicle can be displaced in a direction perpendicular to the direction of travel. The vehicle comprises at least one vehicle seat disposed on the tiltable section of the vehicle and intended for a driver steering the vehicle. The vehicle in general may be any multitrack motor or muscle-powered vehicle such as a road vehicle with wheels, a snowmobile with runners, or a watercraft with foils, having at least three points of support on a ground formed, e.g., by a roadway, snow, ice, or water. The invention further relates to a method for tilting such a vehicle.
2. Description of the Background Art
Multitrack curve-tilting vehicles which owing to their chassis geometry have driving properties similar to those of a single-track vehicle are known in different variants from the prior art. Amongst others, such vehicles have been described in FR 2,550,507, FR 2,616,405, DE 01,063,473, DE 02,707,562, DE 03,546,073, DE 195,13,649, and WO 97/27,071, and are fitted, for instance, with two wheels arranged symmetrically to the vehicle's longitudinal axis, side by side and with a mutual distance, to both sides of the center of gravity, and with a third wheel in the central track in the longitudinal axis, between the two wheels but offset relative to these wheels in or against the direction of travel, with either the two lateral wheels or the central wheel being directionally steerable.
The wheel suspensions of the two lateral wheels are coupled with each other and mounted so as to be able to move essentially in the direction of the vehicle's vertical axis, in such a way that a movement of one of the wheel suspensions in one direction, say, upward, will lead to an opposite movement of the other wheel suspension in the other direction, say, downward. In this way a free tilting of the vehicle about the tilting axis that runs essentially parallel to the vehicle's longitudinal axis can be realized. The reverse coupling can be realized, for instance, mechanically with a steering parallelogram, a balance suspension, or cable lines, hydraulically with two hydraulic cylinders interconnected hydraulically, or electrically with electric motors. It is possible as an alternative to replace the central wheel with two other lateral wheels mobile and coupled in reverse in the direction of the vehicle's vertical axis, which also leads to free tiltability of the vehicle. The lateral wheels that are mounted in parallelogram fashion act as a fictitious single central wheel. In the versions described, pendulum motions and inclinations can be realized largely free of any resistance, and inclining the wheels in parallelogram fashion relative to the ground contributes by gyro-type precession to stabilizing the vehicle in a way similar to a motorcycle or bicycle, hence the driver is provided with a road feeling largely equal to that of the well-known motorcycle feeling. This state of free tiltability of the vehicle will be described in what follows, therefore, as “two-wheel mode”. For the purposes of preventing undesired inclination and tipping over of the vehicle at low speeds or at rest, part of the curve-tilting vehicles known from the prior art have devices restricting or blocking the free mobility of the lateral wheel suspensions at low speeds, and where applicable enabling an active righting or tilting of the vehicle. It is possible then to secure a stabilization of the vehicle at rest by blocking of the free mobility of the lateral wheel suspensions without necessitating an intervention of the driver's legs. This is an advantage more particularly in the case of heavy vehicles which at rest could only be stabilized with a larger effort. In the following, this stable state where a free tilting of the vehicle by countersteering or by a weight shift of the driver is not possible will be designated as “three-wheel mode”, regardless of whether the vehicle is a tilting vehicle having three or more wheels or other elements of support. In this pure “three-wheel mode”, the vehicle can only be tilted actively by a tilting device, but not by a weight shift of the driver or by a centrifugal force attacking directly at the tiltable section, as for instance by the countersteering known from two-wheel vehicles.
It is also known from the prior art that is it advantageous to form a transition zone between the pure two-wheel mode and the pure three-wheel mode. In this intermediate zone the free tiltability is influenced by the partial action of generated tilting forces, and more particularly by forces opposing tilting. In this way it is possible, for instance, by active generation of a force opposing tilting to prevent the vehicle from tipping over when an overly strong tilting is provoked by the driver shifting his weight or steering.
In practice, however, problems are associated exactly with this transition zone from the two-wheel mode, that is, the state of free mobility of the two lateral wheel suspensions, to the three-wheel mode, that is, the state in which a free lateral tilting is prevented by blocking of the free mobility of the lateral wheel suspensions. Because, an automatic active interference with the vehicle's free tiltability is perceived as unpleasant and strange by the driver, and will provoke startled reactions of the driver, sometimes dangerous. While the vehicle at higher speeds has the typical properties of a motorcycle, at low speed or at rest it behaves like a multitrack carriage that cannot be tilted at all by the driver, or only by a targeted but nonergonomic action of the driver.
In WO 95/34,459 a self-stabilising three-wheel vehicle having a power-assisted tilting element for tilting one vehicle section about the vehicle's longitudinal axis is described. The vehicle is self-balancing, and comprises a sensor associated with a directionally steerable wheel and capturing the size and direction of the load that will have to be applied to the directionally steerable wheel in order to produce and/or maintain a change of direction of this wheel during a motion. To this end the sensor is connected with the tilting elements in order to produce a tilting that depends on the sensor's pick-up. Thus, the tilting of the vehicle essentially depends on the steering forces and angles.
In the U.S. Pat. No. 4,368,796 a device for controlling the tilt of a vehicle is described. The change of tilt is accomplished via a pendulum operatively coupled with a tilt change mechanism of the vehicle. In an embodiment said to be preferred, the seat squab of the vehicle seat is pivotable, and fitted with a fork underneath that is able with a certain play to influence the excursion of the pendulum. It is thus possible to deflect the pendulum even in the absence of a centrifugal force or lateral tilt of the vehicle, by the driver strongly laterally shifting his body weight on the driver's seat. It is an essential disadvantage of this system that independently of speed, between the tilt sensing system and the vehicle seat a coupling exists that may lead to dangerous situations, particularly at high speeds where an excessive active interference with the vehicle's tilt is undesirable. It is not possible to provide to the driver the typical driving behavior of a two-wheeled vehicle, since vehicle tilt is achieved in an active way via the pendulum while the driver always is centrally poised on the vehicle, and he may influence the tilting behavior of the vehicle via a displacement of his center of gravity, only when judging that the angle of tilt of the vehicle is not sufficiently large. Because, the tilting behavior of a two-wheeled vehicle is influenced in particular, on the one hand by the gyroscopic forces of the wheels that increase with increasing vehicle speed, and on the other hand by weight shifts of the driver, and the stability of the two-wheeled vehicle increases with increasing vehicle speed. In view of the fork's play that must be provided, it is not at all possible to exercise a sensitive control of vehicle tilt by weight shifts.
From WO 97/27,071, a vehicle is known that has two arms placed side by side and supporting the vehicle above ground. The arms can be coupled by intervening elements so that specific relative positions may be fixed, and in a particular embodiment adjusted actively relative to each other, thus changing the vehicle's tilt. In normal operation called the two-wheel mode, the vehicle described admits pendular motions almost without any resistance, as well as inclined positions, the vehicle behaving as if traveling on a fictitious central rear wheel. In this mode of operation, tilt is achieved essentially by weight shifts of the driver. Two arms are pivoted at a frame of the vehicle. At their far ends, these arms are each provided with one wheel. At the ends of the pivoting axes of the arms facing the center of the vehicle, intervening elements are provided which are fixedly attached to the pivoting axes of the arms, and twist in opposite directions during pendular motions. At the vehicle frame's front end, a front wheel fork is connected with a front wheel and a handle bar. In one embodiment, the two arms are connected with a balance which in its fulcrum is pivoted at the vehicle's frame and which provokes the reverse movements of the arms. The arms may be interconnected via spring-damped legs. In another embodiment, the reverse movements of the arms are produced by circular cable lines. In addition, embodiments are described in WO 97/27,071 where the reverse movements are made possible by a bevel gearing or by a hydraulic compensation. The hydraulic compensation couples the arms that can be adjusted by hydraulic cylinders, so that they will move in opposite directions, the two hydraulic cylinders communicating via a connecting pipe that may include a pressurized gas reservoir for the vehicle's suspension and a check valve for arresting the arms. In addition, various devices for blocking or influencing the pendular motions are shown. Another device for influencing the pendular motions that is described, allows the vehicle to be righted vertically on the roadway via a pincerlike device that is contracted via Bowden cables, so that two props positioned at the two intervening elements are forced into like axial positions.
The document WO 97/27,071 further describes a three-wheeled vehicle in which the intervening elements influencing the pendular motions are levers connected with the levers of a central actuating unit via two tie rods. In one embodiment described, the vehicle includes an arrangement for capturing the speed, a tilt or equilibrium sensor, and additional control buttons to the left and right having a proportional effect for a manual tilt change by the driver. These control buttons may be provided on a handle bar or within the range of the driver's knees, for instance. All commands and response signals are processed in an electrical or electronic control unit and from there forwarded to an actuating unit that is electrical, for instance. With this particular design, specific positions of the arms can be attained at will or by automated remote control, particularly so within a range of speeds up to approximately 4 kmph. At these low speeds, self-stabilization of the vehicle that comes about more particularly through the gyroscopic action of the wheels is still not sufficient for a smooth straight forward motion of the vehicle. In the vehicle described, the reverse mobility of the arms therefore is blocked at a predetermined minimum speed, of for instance 4 kmph, and the vehicle righted into a vertical position from an inclined position that might not be desired. This function relieves the need for the driver to put his feet to the ground, inasmuch as in its normal position the vehicle is kept from tipping over by the lateral wheels. A further improvement in driving properties is achieved according to WO 97/27,071 by a multiple-disk clutch used as a means of intervention between the two ends of the axes of the arms that serve as the intervening elements. With the disk clutch engaged, the reverse movements of the arms are blocked. This blocking action occurs when the vehicle in its normal position falls short of a certain minimum speed. In a further development of this vehicle, an additional tilt sensor in the shape of a pendulum measures a possible lateral sloping of a roadway or a centrifugal force, so that at low speeds the vehicle will always be brought into an upright position or a position that is appropriate for the speed in a bend. Commands of a central actuating unit are translated by the multiple-disk clutch, a mechanical load momentum cutout, and an electric motor with gears. When the speed falls below a minimum of 4 kmph, there is an automatic changeover from free mobility of the arms, that is, the “two-wheel mode”, to an automatic equilibrium control via the equilibrium sensor, so that the vehicle will remain vertical even on a roadway that is sloping laterally. A tilting of the vehicle by weight shifts of the driver is not possible in this mode, since the clutch is engaged and the arms cannot freely move relative to each other. If in this automatic equilibrium control mode a bend is entered, the vehicle will automatically tilt according to speed and radius of the bend, in response to the deflection of the pendulum in the tilt sensor that is caused by the centrifugal force. For initiation of a curve or rapid evasion manoeuvres in this mode, the driver may influence the vehicle's inclination, more particularly in its tendency rather than forcibly, by actuating the left-hand or right-hand control button at the handle bar or knees. The influence produced is proportional to the pressure exerted on the particular control button, but is limited above by a signal of the tilt sensor in order to prevent tipping over.
In the curve-tilting vehicles described above, essentially the entire vehicle is tiltable, while from the prior art and more particularly from WO 98/24,681 or DE 3,226,361 A, curve-tilting vehicles are known that have a twisting two-part part design with a tiltable front part, with a steerable front wheel centrally disposed and with a vehicle seat, and a rear part with two wheels that cannot be tilted. As such vehicles do not tilt in their entirety, and not all wheels assume an inclined position during tilting, so that the gyro precession forces act in different planes and the geometry is also quite different, the driver will experience the driving behavior of a motorcycle to a degree only.
In the document DE 195,01,087 A1, a steerable light vehicle having a driver seat that can be tilted laterally is described, where when driving through a bend the driver can shift his body in the direction of the curve's center while leaning into the seat, or the driver's seat is actively tilted in the direction of the curve's center. The driver's seat and the remainder of the vehicle are operatively coupled in such a way that active or passive tilting of the driver's seat may raise the driving comfort, in that either the driver himself may lean into the bend on his own effort, or the driver's seat is tilted at least partially into the bend. In the latter case, driving states producing the seat readjustment are captured by sensors.
The multitrack curve-tilting vehicles of the prior art described above have the common problem that more particularly at low speeds, a balancing of the vehicle or a tilting as desired by the driver is possible to a degree only, or is perceived as unpleasant or strange by the driver. Some known solutions, it is true, are found to be satisfactory at higher speeds, where the vehicle is in the two-wheel mode and free tiltability of the vehicle is possible, so that the driver essentially is given the feeling of riding a two-wheeled vehicle. When driven at low speeds or at rest, however, known multitrack curve-tilting vehicles are found to be problematic. A use of the feet for stabilization of the vehicle is highly dubious at times, since the mass of some of these vehicles is too large for their safe stabilization, or their closed cabin will prohibit any use of the feet. Tipping over may give rise to important injuries of the legs, arms, and head in particular. The danger of tipping over is in fact reduced by blocking of the free tiltability, that is, by a switching to the three-wheel mode that occurs as a function of speed, and more particularly automatically so, but in this mode a tilting of the vehicle can only be achieved by manipulating actuating elements, or via a tilting sensor triggering an active tilting at low speeds on roadways that slope or bend. An active tilting of the vehicle is perceived as unnatural and unpleasant by the driver, since generically a tilting sensor may trigger the active tilting, only after it has captured an inclined position or centrifugal force. Tilting control via a tilting sensor is definitely problematic, primarily when driving an uneven road at low speeds not admitting free tiltability of the vehicle, where the stabilizing gyroscopic forces of the wheels are too small and the vehicle must be driven in the three-wheel mode. During a sudden tilt of the vehicle as, for instance, when hitting a larger pothole with one of the lateral wheels only, the vehicle will strongly tilt sideways at first. Only at that point this inclined position will be captured by the tilt sensor, so that in a subsequent step the vehicle is actively tilted back into the vertical position. Having passed the pothole, the vehicle being in a tilted state will once more take on an inclined position, so once again the tilt must be adjusted actively via the tilt sensor. It would be possible for the driver recognizing such a situation, for instance prior to driving over an incline, to manually preadjust the tilt by himself, but this possibility is found to be nonergonomic and hardly practical. Even a transition zone between two and three-wheel mode where merely the tilt trend is influenced will resolve matters to a degree only. A further problem arises when entering a bend at low speeds. From a two-wheeled vehicle, the driver would have the habit of moving his weight to the side even prior to the change in direction, or briefly steer into the opposite direction, so that the vehicle leans into the bend to be entered, even prior to the real change of direction. The bend is really taken on while the vehicle tilts, so that the vehicle tipping laterally into the curve is intercepted by the centrifugal force. However, this familiar driving behavior of motorcycles cannot be simulated with known multitrack curve-tilting vehicles at low speeds. As some of these vehicles have a higher weight than motorcycles, they will admit a stabilization or control of tilt by shift of weight of the driver on the vehicle following the human sense of equilibrium, only in part at higher speeds, so that a feeling of driving a motorcycle can be communicated in part, only at higher speeds.
With a driver taking up an eccentric position, where a free tilting by weight shift is not possible at all, only an active tilting is possible. In the prior art, tangible tilting can only be initiated by active manipulation of an actuating unit by the driver or as a reaction to a centrifugal force or steering movement, so that it will not be possible to drive the vehicle by weight shifts like riding a motorcycle.
Known multitrack curve-tilting vehicles meet considerable problems of acceptance by drivers, since at higher speeds in the two-wheel mode they have completely different tilting properties than at lower speeds in the three-wheel mode, inasmuch as the driver may trigger a tilting by shifts of body weight only at higher speeds but not at low speeds.
An anticipating mode of driving providing for a sensitive adjustment of lateral tilt of the vehicle even prior to entering a bend or sloping roadway is possible in an ergonomically acceptable way with multitrack curve-tilting vehicles of the prior art, neither by manual intervention of the driver nor by automatic interventions.